What is the term for workable alluvial deposits of gem materials with economic potential?

The term for workable alluvial deposits of gem materials with economic potential is "placer." Placer deposits are formed through the process of erosion, where water transports valuable minerals and gems from their original source to new locations. Over time, these materials accumulate in stream beds or riverbanks, making them easier to extract.

Placers are significant because they often contain a high concentration of precious stones and metals, making them economically valuable for mining. The natural sorting that occurs through the movement of water helps concentrate the heavier materials in specific locations, leading to deposits that are easier to mine compared to hard rock sources.

In contrast, terms like "vug," "vein," and "seam" refer to different geological formations or contexts. A vug is an irregular cavity in a rock that may contain mineral crystals, while a vein is a distinct, usually planar extension of mineral deposits within rock layers. A seam typically refers to a thin layer of mineral, often associated with coal or other deposits, rather than the specific alluvial context of placers that involves the transport and concentration of gem materials.